The speed of light?

[3rd Enigma]

Could someone tell me-

1) What is the speed of light measured by?

2) What possible factors did play an affect on how the light was measure?

3) Is there proof that nothing can travel faster than the speed of light?

 

 

I ask this because I have done enough research to know how they did it. Yet I still have questions regarding on if people think that the tester speed was a factor into it or rather not. So do people believe that the speed of light is already scientifically proven or perhaps that their measurements may have been altered by the equipment they used.

[NavajoEverclear]

sohray, i know not

[Pinch Paxton]

I think that the speed of light could be wrong, because it could be travelling backwards in time. Imagine a hare running a race, and it travels to the finish line in a time machine. It would pass the line in the future...say 5 seconds into the future, but it would have cheated. It's journey should have taken 3 minutes. Light could be doing a similar thing, so when we test its speed, we are not getting a true reading. My theory is based on tests that show light to be in 2 places at once. This indicates time travel.

 

Pincho.

[Sayonara]

Your theory is not relevant to 3rd Enigma's question, Pinch.

 

(Unless of course it's true, but you really need to prove it is before favouring it over current models )

[JaKiri]

3rd Enigma said in post # :

Could someone tell me-

1) What is the speed of light measured by?

2) What possible factors did play an affect on how the light was measure?

3) Is there proof that nothing can travel faster than the speed of light?

 

 

I ask this because I have done enough research to know how they did it. Yet I still have questions regarding on if people think that the tester speed was a factor into it or rather not. So do people believe that the speed of light is already scientifically proven or perhaps that their measurements may have been altered by the equipment they used.

 

1. Speed = distance / time.

 

2. None. Michaelson-Morely.

 

3. Yes. Time dilation, mass changes, all the other things in SR. Nuclear reactors, too.

[OrderInChaos]

Actually do you have any articles on those proofs? I've had plenty of arguments on this, and I can never think of anything that proves that the speed of light is constant.

[JaKiri]

OrderInChaos said in post # :

Actually do you have any articles on those proofs? I've had plenty of arguments on this, and I can never think of anything that proves that the speed of light is constant.

 

http://directory.google.com/Top/Science/Physics/Relativity/Special_Relativity/?tc=1

[Gavroche]

the speed of light may not be exactly certain, as you said. But it CANNOT be obtained. Any object traveling that speed would be reverted to pure energy (e=mc^2). That means that even if a spacecraft could go that speed, it would instantly be converted into a huge amount of energy. Inobtainable.

[geistkiesel]

Could someone tell me-

1) What is the speed of light measured by?

2) What possible factors did play an affect on how the light was measure?

3) Is there proof that nothing can travel faster than the speed of light?

 

 

I ask this because I have done enough research to know how they did it. Yet I still have questions regarding on if people think that the tester speed was a factor into it or rather not. So do people believe that the speed of light is already scientifically proven or perhaps that their measurements may have been altered by the equipment they used.

 

If I understand your question, the diffeent speeds of different observers all affect measurement. If you are taveling at .8c and I at .5c your measuring equip will be slower and shorter than mine, hence we both measure the speed of light arriving at the same value. My mesured-distanve/time =c= Your-mesured-distance/time. Out ratios are the same but the actual lengths and time referenced to a stationary frame are musch different. That is the theory, if you buy it..

[arivero]

Could someone tell me-

1) What is the speed of light measured by?

2) What possible factors did play an affect on how the light was measure?

3) Is there proof that nothing can travel faster than the speed of light?

 

I ask this because I have done enough research to know how they did it.

 

Do you mean Jupiter moons etc?

[[Tycho?]]

the speed of light may not be exactly certain, as you said. But it CANNOT be obtained. Any object traveling that speed would be reverted to pure energy (e=mc^2). That means that even if a spacecraft could go that speed, it would instantly be converted into a huge amount of energy. Inobtainable.

 

 

Are you sure about this? Why would matter be transformed into energy at c?

[Martin]

Could someone tell me-

1) What is the speed of light measured by?

2) What possible factors did play an affect on how the light was measure?

3) Is there proof that nothing can travel faster than the speed of light?

 

 

I ask this because I have done enough research to know how they did it. Yet I still have questions regarding on if people think that the tester speed was a factor into it or rather not. So do people believe that the speed of light is already scientifically proven or perhaps that their measurements may have been altered by the equipment they used.

 

1) using the metric system it is not possible to measure the speed of light

because the meter (since 1983 convention) has been defined as

the distance light travels in vacuum during a certain small fraction

of a standard second

 

1/2997692458 of a second

 

so the speed in metric units is always equal' date=' by definition, to

299792458 meters (defined this way) per second

 

3) the sky is full of things receding from us faster than c

galaxies have been observed which are receding at several times c.

so this has not been proven impossible

 

on the contrary

 

-------

Do you mean Jupiter moons etc?

 

it can be argued, I guess i would support this viewpoint, that the first

measurement of a fundamental universal constant of nature was made

by Olaus Roemer in Paris around 1675

 

he measured the speed of light (to within an accuracy of about 10 percent) by timing orbits of Jupiter's moon Io

 

he measured it in terms of the distance of the earth to the sun which was known in conventional earth units (miles, leagues, furlongs etc) at that time only very roughly (to within about 10 percent)

and in terms of traditional earth-rotation-based time.

 

arivero just referred to Roemer's measurement, which reminded me

 

there is a plaque on the front of the old Observatoire de Paris building

commemorating Roemer's measurement of the speed of light in 1675

 

what is the greatest or most memorable thing that ever happened in paris?

maybe Francois Villon's poems, maybe the paintings of the Impressionists,

maybe the making of a favorite movie, you have to decide for yourself.

 

But when villon and the impressionists are forgotten people will probably still remember that a young Danish astronomer at the Observatoire measured the speed of light-----if there is still a civilization then which is capable of remembering anything.

 

It was a first.

 

(although galileo had tried to do it in a farcical manner some 50 years earlier)

[swansont]

'']Are you sure about this? Why would matter be transformed into energy at c?

 

It wouldn't. I imagine the concept of requiring infinite energy to travel at c for massive objects, and only massless objects - which have purely kinetic energy - travelling at c, can somehow be tortured and mangled into that statement. But it's not something I would care to watch.

[senexa]

Molecular Expressions has a really good article on the history of measuring the speed of light and its properties in vacuum and other media.

 

But, the article concludes, "Physicists point out that the actual speed of light as measured by Roemer and his followers has not significantly changed, but rather point to a series of refinements in scientific instrumentation associated with increases in precision of the measurements utilized to establish the speed of light."

 

http://micro.magnet.fsu.edu/primer/lightandcolor/speedoflight.html

[[Tycho?]]

It wouldn't. I imagine the concept of requiring infinite energy to travel at c for massive objects, and only massless objects - which have purely kinetic energy - travelling at c, can somehow be tortured and mangled into that statement. But it's not something I would care to watch.

 

Yeah I thought so, thanks for clearing that up.

[qazibasit]

well i think many ppls have a wrong concept that speed of light will lead them to future or in the past but instead the speed of light will only stops the time if you are faster than the speed of light in positive direction then you will lead to the future and you are faster than light in negative quadrant then you will go in the past .

 

well MrL_JaKiri is right that speedd=distance/time

 

well the speed of light is prooved by the super computer.

[[Tycho?]]

...

3) the sky is full of things receding from us faster than c

galaxies have been observed which are receding at several times c.

so this has not been proven impossible

...

 

 

Um' date=' [i']what[/i].

 

I call bullshit on this one, this goes against everything I know on relativity. If you can prove me wrong, by all means do so.

[JaKiri]

']Um' date=' [i']what[/i].

 

I call bullshit on this one, this goes against everything I know on relativity. If you can prove me wrong, by all means do so.

 

That is most definitely wrong; especially given the universe is expanding at sublight speeds (at the moment, as far as my memory tells me)

[[Tycho?]]

That is most definitely wrong; especially given the universe is expanding at sublight speeds (at the moment, as far as my memory tells me)

 

Yeah, it definately is, otherwise relativity would have been thrown out the window when one of its principal predictions was broken. Which it hasn't been.

[Dave]

I have to say it goes against everything I've ever been taught, so I'm in opposition.

 

Not quite sure where he got that one from.

[DeoxyriboNucleicAcid]

Maybe Martin means that if you move towards a source of light, it would "relatively" be moving faster than the speed of light.

If a rocket ship launches into space toward the sun, the rays will apear to move faster than the speed of light. Speed is relative. We see this in the red shift/ doppler effect, I think because of changes in frequency, correct?

[Dave]

Nope; at relativistic speeds you use the relativistic doppler effect, and for relative speeds there's a whole set of equations to stop the speed exceeding c.

[Martin]

Martin:

3) the sky is full of things receding from us faster than c

galaxies have been observed which are receding at several times c.

so this has not been proven impossible

...

 

 

[Tycho?]:

Um, what.

I call bullshit on this one, this goes against everything I know on relativity. If you can prove me wrong, by all means do so.

 

 

JaKiri:

That is most definitely wrong; especially given the universe is expanding at sublight speeds (at the moment, as far as my memory tells me)

 

[Tycho?]:

Yeah, it definately is, otherwise relativity would have been thrown out the window when one of its principal predictions was broken. Which it hasn't been.

 

 

Dave:

I have to say it goes against everything I've ever been taught, so I'm in opposition.

 

Not quite sure where he got that one from.

--------------

 

Hi Tycho, Jakiri, Dave,

 

I am telling you a feature of the standard model cosmology that mainstream professional cosmologists pretty much all use.

It is based on 1915 General Relativity and the Friedmann model derived from it in the 1920s by making simplifying assumptions (isotropy, homogeneity). It leads to the definition of the Hubble parameter

(now pretty accurately measured) and to the socalled "big bang model"

or the prevailing LambdaCDM model. there is a pretty general consensus

on the basic features

 

One of these basic features is FTL recession speeds.

It is a popular confusion that these are forbidden since special relativity does not apply over great distances of curved space. it is a local theory.

Nothing can catch up to and pass a photon! Nothing can come whizzing past earth at FTL speed!

But that does not mean that the distance to a remote galaxy cannot be increasing at a FTL rate.

in fact, General Relativity predicts FTL recession speeds

 

the popular confusion about this has been dealt with in a remedial article by Tammy Davis and Chuck Lineweaver. Lineweaver was one of the principal investigators in charge of COBE (the first map of the CMB) and is a world class authority Tammy is one of his PhD students. They are mainstream and you can trust them. At least they took the trouble to try to counter the confusion that so many people have about superluminal expansion speeds.

Their article is called "Expanding Confusion"

I will get the arxiv number.

 

To my mind one of the best ways to get over the misconception that you cant have superlum. recession speeds is to use an algorithm published by the magazine Sky and Telescope-----S&T is probably familiar to many people here.

this program calculates distances and recession speeds for a given redshift z. You put in the z (and parameters like H and Lambda for dark energy) and it calculates the recession speed at present and also what it was when the object emitted the light which we are now receiving.

 

An astro professor at the univ. of iowa named Siobahn Morgan has put the Sky and Telescope program into a java online calculator at her website for her astronomy students to use and it will give you all the superluminal recession speeds you want

 

Even for z = 2 the thing is now receding FTL even as we receive the light from it that it emitted a few billion years ago. the calculator will supply the particulars. I will get the URL for it

 

The consensus model of cosmology that virtually everybody uses---the mainstream professional people I mean----would break down if you didnt allow FTL recession speeds

 

recession speeds are a rate that already large distances are increasing

 

they are a different kind of speed from local encounter speeds (which are governed by special rel)

[Martin]

Here are some online cosmology calculators

Ned Wright who teaches cosmology at UCLA, and

also Siobahn Morgan who teaches astronomy at Iowa

check out their homepages. ned has a cosmology FAQ that is

world famous! has been translated into various languages.

 

Here are two good online cosmology calculators

 

Siobahn Morgan's

http://www.earth.uni.edu/~morgan/ajjar/Cosmology/cosmos.html

 

and Ned Wright's

http://www.astro.ucla.edu/~wright/CosmoCalc.html

 

homepages for Morgan

http://www.earth.uni.edu/smm.html

and Wright

http://www.astro.ucla.edu/~wright/intro.html

 

To use Siobahn's calculator put Lambda = 0.73

Omega = 0.27

H = 71 (or leave her default value of H = 70, nearly the same)

those are the dark energy and the matter densities as fractions of rho crit,

and H is the present value of the Hubble parameter

 

then put in any redshift z,

like z =1 or 3 or 10 and it will tell you how far away the thing

was when it emitted the light we are now getting from it

and how far away it is now

and how fast it was receding then

and how fast it is receding now, at the present moment

[Martin]

this might interest Dave especially

 

one of the first things you learn in a basic astro course is that the

cosmological redshift is not a doppler shift

 

it is caused by the stretching out of space while the light was in transit

 

Eric Linder has some online cosmology notes that explains this

he teaches at UC Berkeley and has a textbook out that is an Intro to Cosmology

 

it you try to explain it as a doppler shift you get into trouble because the recession speed of the thing changes substantially over time

 

what matters to the wavelength is how much space expanded (the Friedmann model, the FRW, friedmann robertson walker metric) while the light was on its way.

 

so the first thing they give you is a different, non-doppler, formula for the redshift.

-----------------

 

then there is the Hubble law

 

v = Hd

 

the H is the value of the hubble parameter today

the v is the recession velocity of the thing at this moment

the d is the distance at the present moment

 

the definitions depend on the FRW metric, which is the standard,

and the Friedmann equations

H in fact appears as (a'/a) in one of the friedmann equations

(the one that defines rho crit, the critical density)

 

because of the linearity of the Hubble law, you can see that if d is large enough you simply have to get v exceding light.

but it is just a recession velocity, nobody's spaceship catches up to a photon!